A wide variety of antennas are used to transmit and/or receive signals at microwave or millimeterwave frequencies. These signals (commonly referred to as radio frequency (RF) signals) often pass through phase shifters between a transceiver circuit and the radiating elements of the antenna. In some applications, a phase shifter is employed to assist in steering an output of the radiating element of a phased array radar assembly. However, phase shifters are also employed in other types of radars and communication devices.
A common type of phase shifter is comprised of a switched path circuit having a number of serially connected stages, each of which form a 50 ohm system. Each stage includes two phase delay lines of different length. For each stage, the RF signal is passed through a selected one of the phase delays by using switches to select a desired path from an input of the switched path circuit to an output of the switched path circuit. Typically, each stage has one delay line dedicated to zero phase shift and the other to a predetermined desired amount of delay. Each stage includes a switching mechanism for connecting an input of the stage to a desired one of the phase delay lines. Another switching mechanism (or recombining switch) functions to connect the selected delay line to an output of the stage. U.S. Pat. No. 6,281,838 includes an example of the foregoing switched path circuit as well as a base-3 embodiment (having three phase delays per stage) of a switched path circuit.
The Applicants have found that switched path phase shifters using MEMS contact switches have limited power handling capability. More specifically, as the RF current associated with the signal increases, the amount of power dissipation within the switches of the switched path phase shifter increases leading to physical failure of the switch devices. The primary failure mechanism has been determined to be power dissipation in the switch contacts.
Accordingly, there exists a need in the art for higher performance phase shifters for use in RF applications and especially in RF applications having relatively high power levels.